Sandbanks, sandwaves and megaripples on Spitsbergenbanken, Barents Sea

Recently acquired multibeam echosounder data from the shallowest part (26–53 m depth) of Spitsbergenbanken in the western Barents Sea reveal a variety of bedforms, including megaripples, sandwaves and sandbanks. The bedforms exhibit varying degrees of superimposition and differ in their age of formation and present depositional regime, being either active or moribund. These are the first observations of co-occurring current induced bedforms in the western Barents Sea and provide evidence of a high energy environment in the study area. The bedforms indicate both sediment erosion and transport and confirm that there is enough sand available in this area to maintain them. Such conditions are not known to be common in the western Barents Sea and reflect the unique oceanographic and benthic environment of Spitsbergenbanken.publishedVersio

Late Weichselian and Holocene sedimentary processes and environments in Billefjorden, Svalbard

Three sediment cores, swath multibeam bathymetry data and high-resolution seismic data from Billefjorden, Svalbard have been analysed for a better understanding of the Late Weichselian and Holocene glacier activity as well as sedimentary process and glacigenic deposits in the fjord. The data reveal that glacial linear features were generated in the central part of Billefjorden while it was filled with ice draining the Svalbard-Barents Sea ice sheet during the Last Glacial. A till in the bottom of a sediment core from the central part of the fjord is inferred to have been deposited before the ice front retreated into Billefjorden around 11230 cal. years BP. An overlying glacimarine unit deposited between c. 11230 and 11200 cal. years BP indicates that the glacier retreated from central parts of the fjord to the fjord head in approximately 30 years. Annual recessional moraines deposited during this period suggest that the glacier front retreated approximately 330 m/ year at the end of the last Glacial. High concentration of shells, low amounts of IRD and XRD results indicate a Holocene climatic optimum between c. 11200 – 7930 cal. years BP in which Nordenskiöldbreen was most likely much smaller than it is at present. XRD results and comparatively high amounts of IRD point to a complex pattern of ice rafting between c. 7930 and 3230 cal. BP. IRD deposited before c. 5470 cal. years BP was most likely transported by sea ice, whereas IRD after 5470 cal. years points towards a growth of Nordenskiöldbreen. The time after c. 3230 is mainly characterised by suppressed rafting of sea ice and icebergs because of the possible presence of multi-year shorefast sea ice during the Neoglacial maximum. Glacial lineations on a bedrock terrace in the inner fjord were formed during a Neoglacial advance of Nordenskiöldbreen. Iceberg ploughmarks and recessional moraines were most likely generated during the retreat after the maximum Neoglacial extent of Nordenskiöldbreen. Mass-transport activity in Billefjorden probably occurred throughout the entire Holocene. There might haven been an increased mass-transport activity shortly after the deglaciation of the fjord, because high rates of isostatic uplift might have caused seismic activity. Other triggering mechanisms include the development of oversteepened slopes by high sediment supply and the pushing of sediments at the grounding line of the glacier. Pockmarks in the central part of the fjord were most likely generated by the seepage of thermogenic gas along the Billefjorden fault zone

Mass-movements on the continental slope offshore Lofoten, Northern Norway

Swath bathymetry, side-scan sonar, sub-bottom profiler and seismic data from the continental slope offshore the Lofoten Islands, northern Norway reveal smaller-scale mass movements in water depths between 1100 and 2500 m. These mass movements have volumes of 0.061 to 8.7 km3 and are interpreted as translational slides involving spreading and multi-phase retrogression. The spatial variation in failure style is inferred to have been caused by the activation of different glideplanes (12.5-130 mbsf) within the thicker and more mounded contouritic deposits in the north-east of the study area. Data from a sediment core show that the shallowest style of mass movement (12.5 mbsf), was initiated within contouritic sediments characterized by high sensitivities and water contents. This unit overlies a plumite interval characterized by dilative behavior with pore pressure decrease with increasing shear strain and high undrained shear strength. As such, it is the difference in geotechnical properties which indicates that the interface between these units acts as the basal glide plane, with deformation in the weaker overlying unit. The mass movements in the study area are inferred to have been triggered by undercutting and removal of support at the foot of the slope due to large-scale mass movements that have occurred immediately south of the study area, such as the Trænadjupet or Nyk slides. Furthermore, a network of 2D seismic data reveals the presence of several paleo-canyons. The data illustrate that canyon formation is more extensive then previously thought. These paleo-canyons are buried by an extensive contourite drift interpreted to be a continuation of the Lofoten Drift. The distribution of the drift indicates changes in the depth and strength of paleo-currents. Mass movements only occur in the upper part of the sequence, most likely after the onset of the Pleistocene

Formation of a large submarine crack during the final stage of retrogressive mass wasting on the continental slope offshore northern Norway

High-resolution swath-bathymetry data integrated with sub-bottom profiles and single-channel seismics reveal an 18 km long, up to 1000 m wide and 10-15 m deep crack located approx. 4 km upslope from a slide scar on the continental slope off northern Norway. This crack is formed by subsidence of the sea-floor sediments to a depth of 120 m due to downslope movement of a ~80 km2 large sediment slab that represents the final stage of retrogressive mass wasting in this area. From its morphological freshness, the crack this is inferred to have formed sometime during the last 13 cal. ka BP. These findings add to our understanding of the origin of sea floor cracks on passive continental margins where explanations as slip of normal faults or gas expulsion from the dissociation of gas hydrates previously have been suggested for the formation of cracks in similar settings

Sandbanks, sandwaves and megaripples on Spitsbergenbanken, Barents Sea

Recently acquired multibeam echosounder data from the shallowest part (26–53 m depth) of Spitsbergenbanken in the western Barents Sea reveal a variety of bedforms, including megaripples, sandwaves and sandbanks. The bedforms exhibit varying degrees of superimposition and differ in their age of formation and present depositional regime, being either active or moribund. These are the first observations of co-occurring current induced bedforms in the western Barents Sea and provide evidence of a high energy environment in the study area. The bedforms indicate both sediment erosion and transport and confirm that there is enough sand available in this area to maintain them. Such conditions are not known to be common in the western Barents Sea and reflect the unique oceanographic and benthic environment of Spitsbergenbanken

Sandbanks, sandwaves and megaripples on Spitsbergenbanken, Barents Sea

Recently acquired multibeam echosounder data from the shallowest part (26–53 m depth) of Spitsbergenbanken in the western Barents Sea reveal a variety of bedforms, including megaripples, sandwaves and sandbanks. The bedforms exhibit varying degrees of superimposition and differ in their age of formation and present depositional regime, being either active or moribund. These are the first observations of co-occurring current induced bedforms in the western Barents Sea and provide evidence of a high energy environment in the study area. The bedforms indicate both sediment erosion and transport and confirm that there is enough sand available in this area to maintain them. Such conditions are not known to be common in the western Barents Sea and reflect the unique oceanographic and benthic environment of Spitsbergenbanken